The use of diaphragms in fluid pumps is well known. Diaphragm pumps offer several advantages over conventional piston pumps, among which are a resistance to leakage and a decreased number of parts required. In such pumps, the diaphragms are not driven directly, but are driven through a pressure medium or "drive fluid", which is contained within a drive chamber. A typical drive fluid is air which is used to cycle the diaphragm back and forth. The diaphragm forms a boundary between the drive chamber and a pump chamber which contains the fluid to be pumped. One disadvantage of known diaphragm pumps is the risk of contamination of the pump fluid by leaking drive fluid. If the diaphragm seal is defective or develops a leak due to wear of the diaphragm material, drive fluid may escape to the pump chamber, where it may commingle with and contaminate the fluid to be pumped. Such contamination is particularly undesirable in applications where the purity of the pumped fluid is critical. Another disadvantage is a significant reduction in pump efficiency if drive fluid pressure in the drive chamber is continually lost because of a diaphragm leak.
Attempts have been made to produce highly durable and wear resistant diaphragms for such pump applications. Conventional single material diaphragms made out of material such as elastomer are highly flexible and resilient providing excellent pumping characteristics, but are not exceptionally durable.
Fabric reinforcement has been added to elastomer material such as Neoprene in attempting to increase the durability or wear characteristics of the diaphragm. This has been proved to be insufficient for many applications wherein the fluid to be pumped requires that the diaphragm be resistant to chemical degradation and surface abrasion and yet remain flexible and durable. Such known diaphragms are relatively flexible and strong and provide some abrasion resistance but are not chemically resistant to many materials or fluids. An example of such a fabric reinforced diaphragm is disclosed in International Patent Publication No. W097/36092 which is assigned to Wilden Pump & Engineering Co.
The assignee of the present invention has previously developed the use of back-up type diaphragms having an elastomer support diaphragm and a diaphragm with fluorocarbon (such as TEFLON.RTM.) as a pump overlay in air operated double diaphragm pumps. Such a diaphragm has an elastomeric diaphragm and a fluorocarbon diaphragm overlay placed on but not bonded to the side facing the fluid to be pumped. The support diaphragm is subjected to a bulk of the stress from the cyclic operation of the diaphragm and the fluorocarbon overlay provides the chemical resistance. An additional example of this type of layered diaphragm is disclosed in U.S. Pat. No. 5,349,896 which is assigned to W.L. Gore & Associates, Inc. The '896 patent additionally discloses bonding the two layers together.
One problem with the overlay diaphragm construction is that the TEFLON overlay material is not particularly strong, flexible or abrasion resistant. To make the TEFLON material more abrasion resistant the material must be thickened to compensate for these shortcomings. By making the material thicker, it exacerbates another problem with fluorocarbon materials in that they are not very flexible in their natural state. Thus, a fluorocarbon overlay over an elastomeric diaphragm which is adequately abrasion resistant is not very flexible and hence not very durable during cyclic operation. A thinner walled TEFLON overlay may provide at best adequate durability during flex of the diaphragm but does not provide adequate abrasion resistance to the fluids within the pump.
Another problem with the TEFLON overlay material is that it is not sufficiently strong. When a TEFLON material is subjected to repeated flexing or stress, it has insufficient elasticity or elastic memory so that when the stress is released it does not return completely to its original shape. Therefore, as the TEFLON overlay is stressed it becomes thinner over time further reducing its abrasion resistance and strength.